#* Version:		2.0
#* Date: 		10/28/2022
#* Time: 		17:27 PM
#* Issue: 		Unable to process multiple computers with single output
#* Solution:	Changed the script to use a pipleple process where data is 
#*              collected then outout as objects.
#*
#*=============================================================================
Param(
    [string]$CsvList,
    [string]$NameColumn = 'Name',
    [switch]$ExportResults
)
#*=============================================================================
#* FUNCTIONS
#*=============================================================================

Function Get-ServerUptime {
    <#
    .SYNOPSIS
	    Calculates the percent uptime for the given server.

    .DESCRIPTION
	    The getServerUpTime script returns the uptime for a remote or local 
	    computer.
	
	    Without parameters, getServerUptime returns the uptime for the local 
	    computer over the past 30 days.
	
    .PARAMETER ComputerName
	    Calculates the percent uptime for the specified computers. The default is 
	    the local computer.

	    Type the NetBIOS name, an IP address, or a fully qualified domain name of 
	    a computer. To specify the local computer, type the computer name, a dot 
	    (.), or "localhost".
	
    .PARAMETER NumberOfDays
	    The function will calculate the uptime of the computer for the past N days,
	    where N equals the value of NumberOfDays.
	
    .EXAMPLE
	    PS C:\> Get-ServerUptime
	    Retrieving shutdown and startup events from MyLaptop for the past 30 days...
	    WARNING: This could take several minutes!
	
	    Name            : MyLaptop
        Status          : Online	    
        NumOfDays       : 30
	    NumOfCrashes    : 1
	    NumOfReboots    : 18
	    MinutesDown     : 16 hours 20 minutes           
	    MinutesUp       : 703 hours 40 minutes
	    PercentDowntime : 2.2675%
	    PercentUptime   : 97.7325%
	
    .EXAMPLE
	    PS C:\> Get-ServerUptime -ComputerName SVR001 -NumberOfDays 365 -Raw
	    Retrieving shutdown and startup events from SVR001 for the past 365 days (time will be in raw format)...
	    WARNING: This could take several minutes!
	
	    Name            : SVR001
	    Status          : Online
        NumOfDays       : 365
	    NumOfCrashes    : 1
	    NumOfReboots    : 13
	    MinutesDown     : 63.15
	    MinutesUp       : 525,536.85
	    PercentDowntime : 0.0120 %
	    PercentUptime   : 99.9880 %

    .EXAMPLE
        PS C:\> Get-ADComputer -filter * -Properties * | Select -ExpandProperty Name  | Get-ServerUptime -ShowProgress | Format-Table
        Retrieving shutdown and startup events all systems in AD for the past 365 days (Progress of each server will display)...
        WARNING: This could take several minutes!

        Name         Status  NumOfDays NumOfCrashes NumOfReboots MinutesDown         MinutesUp            PercentDowntime PercentUptime Details             
        ----         ------  --------- ------------ ------------ -----------         ---------            --------------- ------------- -------             
        Lab-dc2      Online         30            1           13 16 hours 20 minutes 703 hours 40 minutes 2.2675%         97.7325%      {Retrieving shutd...
        LAB-DC3      Online         30            2           26 32 hours 39 minutes 687 hours 21 minutes 4.5350%         95.4650%      {Retrieving shutd...
        LAB-SCCM     Denied                                                                                                             {No access to the...
    
    .EXAMPLE
        PS C:\> Get-ADComputer -Filter "OperatingSystem -Like '*Windows Server*' -and Enabled -eq 'True'" | Export-Csv $env:USERPROFILE\desktop\serverlist.csv -NoTypeInformation
        PS C:\> $CsvList = "$env:USERPROFILE\desktop\serverlist.csv"
        PS C:\> $CsvList.Name | Get-ServerUptime -ShowProgress -Raw
        Retrieving shutdown and startup events all systems in AD export to list (Progress of each server will display)...
        WARNING: This could take several minutes!

    .EXAMPLE
        PS C:\> 'LAB-DC3','LAB-DC2','LAB-OFFCA','LAB-WAP','LAB-NDES' | Get-ServerUptime -Verbose | Format-Table
        Retrieving shutdown and startup events all listed systems in verbose data and formatted as a table...
        WARNING: This could take several minutes!
    #>
    [cmdletbinding()]
   	Param(
        [Parameter(Mandatory=$false,ValueFromPipeline=$true)]
        [string[]]$ComputerName =$env:COMPUTERNAME,
        [int] $NumberOfDays = 30,
        [switch]$Raw,
        [switch]$ShowProgress
	)
    Begin{
        $Status = @()
        [timespan]$downtime = 0
        # Count the number of system crashes
		$crashCounter = 0	
		# Count the number of reboots
		$rebootCounter = 0
        $events = $null
    }
	Process {
        #$Name = $ComputerName[0]
        Foreach($Name in $ComputerName){
            
            If($ShowProgress){Write-Host ('Please wait to generating uptime data for [{0}]...' -f $ComputerName) -NoNewline}

            # Create a custom object to hold the results
		    $results = "" | Select-Object Name, Status, NumOfDays, NumOfCrashes, NumOfReboots, MinutesDown, MinutesUp, PercentDowntime,PercentUptime,Details
            $results.Details = @()

            # Ensure the server is reachable
		    if (Test-Connection -ComputerName $Name -Count 1 -TimeToLive 10 -Quiet) {
		
			    # Ensure that this is a Windows server that we are working with and 
			    # that we have the appropriate permissions
			    if (Test-Path -Path "\\$Name\C$") 
			    {
				    # Did the user pass in an appropriate value for number of days?
				    # If not, we will assume the default, 30 days.  If the value is
				    # more than 365, we use 365 as the maximum.
				    if ($NumberOfDays -le 0) 
				    {
					    $NumberOfDays = 30
					    $results.Details += "Defaulting to 30 days..."
				    } 
				    elseif ($NumberOfDays -gt 365) 
				    {
					    $NumberOfDays = 365
					    $results.Details += "Using maximum value (365 days)..."
				    } 
				
      			
      			    # We begin by assuming 100% uptime.  We will calculate effective 
      			    # uptime by subtracting downtime from this value
				    [timespan]$uptime = New-TimeSpan -Days $NumberOfDays
				    $currentTime = Get-Date
				    $startUpID = 6005
				    $shutDownID = 6006
				    $minutesInPeriod = $uptime.TotalMinutes
				    $startingDate = (Get-Date).adddays(-$NumberOfDays)
				
				    # Output some useful debugging info
                    Write-Verbose "========================================"
                    Write-Verbose "Computer:       $Name"				    
                    Write-Verbose "Uptime:         $uptime"
				    Write-Verbose "Downtime:       $downtime"
				    Write-Verbose "Current time:   $currentTime"
				    Write-Verbose "Start time:     $startingDate"
				    
				
				    # Warn the user that this could take a while
				    $results.Details += "Retrieving shutdown and startup events from "
				    $results.Details += "$Name for the past $NumberOfDays days..."
				    $results.Details += "This could take several minutes!"
				
				    # Create a new PSSession to be used throughout the script
				
				    # Remotely retrieve the events from the system event log that 
				    # occurred in the past $NumberOfDays days ago
				    $events = Invoke-Command $ComputerName $Name -ScriptBlock {`
					    param($days,$up,$down) 
					    Get-EventLog `
						    -After (Get-Date).AddDays(-$days) `
						    -LogName System `
						    -Source EventLog `
					    | Where-Object { 
						    $_.eventID -eq  $up `
						    -OR `
						    $_.eventID -eq $down }
				    } -ArgumentList $NumberOfDays,$startUpID,$shutDownID -ErrorAction Stop
				
				    # Create a new sorted array object
				    $sortedList = New-object system.collections.sortedlist
				
				    # If there are shutdown or startup events, add them to the 
				    # sorted array, otherwise add zeroes to the array as placeholders
				    if ($events.Count -ge 1) 
				    {
					    ForEach($event in $events)
					    {
						    $sortedList.Add( $event.timeGenerated, $event.eventID )
					    } #end foreach event
				    } 
				    else 
				    { # There were no shutdown events during this time period
					    $sortedList.Add( 0, 0 )
				    } 
				
				    # Iterate through the sorted events and add up the downtime
				    For($i = 1; $i -lt $sortedList.Count; $i++ )
				    { 
					    if(	($sortedList.GetByIndex($i) -eq $startupID) -AND ($sortedList.GetByIndex($i) -ne $sortedList.GetByIndex($i-1)) ) 
					    { # There was a shutdown event paired to the startup event, 
					      # thus it was a planned shutdown
					  
						    # Write each event to the Debug pipeline
						    Write-Verbose "Shutdown `t $($sortedList.Keys[$i-1])" # Shutdown
						    Write-Verbose "Startup  `t $($sortedList.Keys[$i])" # Startup
						
						    # Outage duration = startup timestamp - shutdown timestamp
						    $duration = ($sortedList.Keys[$i] - $sortedList.Keys[$i-1])
						    $downtime += $duration
						    Write-Verbose "           Outage duration: $duration"
						    Write-Verbose "           Downtime is now: $downtime"
						    Write-Verbose ""
						
						    # Bump the reboot counter
						    $rebootCounter++
					    } 
					    elseif(	($sortedList.GetByIndex($i) -eq $startupID) -AND ($sortedList.GetByIndex($i) -eq $sortedList.GetByIndex($i-1)) )
					    { 	# This was an unplanned outage (a system crash). 
						    # Basically this means that we have 2 startup events 
						    # with no shutdown event
												
						    # Get the date from the event stating that there was an
						    # unexpected shutdown
						    $tempevent = Invoke-Command $ComputerName $Name`
							    -ScriptBlock {`
								    param([datetime]$date, [string]$log)
								    Get-EventLog `
									    -Before $date.AddSeconds(1) `
									    -Newest 1 `
									    -LogName System `
									    -Source EventLog `
									    -EntryType Error `
									    -ErrorAction "SilentlyContinue" | `
								    Where-Object {$_.EventID -eq 6008}
							    } -ArgumentList $sortedList.Keys[$i],$($eventlog.log)
						
						    # The 6008 event has the data we're looking for in the 
						    # ReplacementStrings property but the date portion of the
						    # data has a special character that we need to remove,
						    # [char]8206, so we replace it with a space.
						    $lastEvent = [datetime](`
							    ($tempevent.ReplacementStrings[1]).Replace([char]8206, " ")`
							    + " " + $tempevent.ReplacementStrings[0])
						
						    # Write each event to the Debug pipeline
						    Write-Verbose "CRASH    `t $lastEvent"
						    Write-Verbose "Startup  `t $($sortedList.Keys[$i])" # Startup
						
						    # Calculate downtime = Startup timestamp - Last event 
						    # written to any log timestamp
						    $duration = ($sortedList.Keys[$i] - $lastEvent)
						    $downtime += $duration
						    Write-Verbose "           Outage duration: $duration"
						    Write-Verbose "           Downtime is now: $downtime"
						    Write-Verbose ""
						    Write-Verbose "--------------------------------------"
						    # Bump the crash counter
						    $crashCounter++						
					    } 
				    } #end for item
				
				    # Subtract downtime from calculated uptime to get true uptime
				    $uptime -= $downtime
				
				    
				    $results.Name = $Name
				    $results.NumOfDays = $NumberOfDays
				    $results.NumOfCrashes = $crashCounter
				    $results.NumOfReboots = $rebootCounter
                    If($Raw){
                        $results.MinutesDown = [math]::Round($downtime.TotalMinutes)
                        $results.MinutesUp = [math]::Round($uptime.TotalMinutes)
                    }Else{
                        $results.MinutesDown = Format-Duration -Duration ([math]::Round($downtime.TotalMinutes))
                        $results.MinutesUp = Format-Duration -Duration ([math]::Round($uptime.TotalMinutes))
                    }
				    $results.PercentDowntime = "{0:p4}" -f (1 - $uptime.TotalMinutes/$minutesInPeriod)
				    $results.PercentUptime = "{0:p4}" -f ($uptime.TotalMinutes/$minutesInPeriod)
                    $results.Status = 'Online'

				    $Status += $results
				    #return $results | Format-Table
                    If($ShowProgress){Write-Host 'Done' -ForegroundColor Green}
      		    } 
      		    else 
      		    {
      			    # This usually means that you've encountered a server that 
      			    # is not running Windows, like a Linux server
      			    $results.Details += "No access to the default share - \\$Name\C`$"

                    
				    $results.Name = $Name
                    $results.Status = 'Denied'
                    $Status += $results
                    $results = $null

                    If($ShowProgress){Write-Host 'Failed' -ForegroundColor Red}
      		    } 
      	    } 
      	    else 
      	    { # This server is not online
      		    $results.Details += "Unable to connect - $Name"

                # Create a custom object to hold the results
				    
				    $results.Name = $Name
                    $results.Status = 'Offline'
                    $Status += $results
                    $results = $null

                    If($ShowProgress){Write-Host 'Off' -ForegroundColor Yellow}
      	    } 
        } # end loop
    } # end Process
    End{
        return $Status
    }
}

Function Format-Duration ($Duration) {
    $TimeSpan = New-TimeSpan -Minutes $Duration
    $h = $TimeSpan.Days * 24 + $TimeSpan.Hours
    $m = $TimeSpan.Minutes
    if($h -gt 0){"$h hours $m minutes"}
    else{"$m minutes"}
}
#*=============================================================================
#* MAIN
#*=============================================================================

If( $(try { Test-path $CsvList } catch { $false }) ){
    $SystemList = Import-Csv $CsvList
    $Export = $SystemList.$NameColumn | Get-ServerUptime -ShowProgress -Raw
}Else{
    '-----------------------------------------------------'
    write-host 'Run for single server: ' -ForegroundColor Cyan -NoNewline
    write-host 'Get-ServerUptime ' -ForegroundColor White -NoNewline
    write-host '-Computername ' -ForegroundColor Gray -NoNewline
    write-host "'DC01'" -ForegroundColor Cyan
    write-host 'Run for multiple servers: ' -ForegroundColor Cyan -NoNewline
    write-host "'LAB-DC3','LAB-DC2','LAB-OFFCA','LAB-WAP','LAB-NDES' " -ForegroundColor DarkCyan -NoNewline
    write-host '| ' -ForegroundColor Gray -NoNewline
    write-host "Get-ServerUptime " -ForegroundColor White -NoNewline
    write-host '-ShowProgress ' -ForegroundColor Gray -NoNewline
    write-host '| ' -ForegroundColor Gray -NoNewline
    write-host "Format-Table" -ForegroundColor White
    write-host 'Run from a server list: ' -ForegroundColor Cyan -NoNewline
    write-host ".\Get-ServerUptime.ps1 " -ForegroundColor White -NoNewline
    write-host '-CsvList ' -ForegroundColor Gray -NoNewline
    write-host '$env:UserProfile' -ForegroundColor Cyan -NoNewline
    write-host '\Desktop\serverlist.csv ' -ForegroundColor DarkCyan -NoNewline
    write-host '-ExportResults' -ForegroundColor White
    write-host 'Review more examples: ' -ForegroundColor Cyan -NoNewline
    write-host "Get-Help " -ForegroundColor White -NoNewline
    write-host "Get-ServerUptime" -ForegroundColor DarkCyan -NoNewline
    write-host " -examples" -ForegroundColor White
    '-----------------------------------------------------'
}

If($ExportResults){
    $Filename = "SystemExport_$(Get-Date -Format 'yyyy-MM-dd_Thh-mm-ss-tt').csv"
    If($CsvList){
        $ExportFolder = Split-Path $CsvList -Parent
    }Else{
        $ExportFolder = "$env:USERPROFILE\desktop"
    }
    
    $Export | Export-Csv "$ExportFolder\$Filename" -NoTypeInformation
    Write-host ("Exported to {0}" -f "$ExportFolder\$Filename") -ForegroundColor Cyan
}